In wellbore construction and completion operations, a wellbore is initially formed to access hydrocarbon-bearing formations (i.e., crude oil and/or natural gas) by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a tubular string, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table and Kelly on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. A pumping system is used to inject drilling fluid through the top drive or Kelly, down the drill string, through the rotating drill bit, and back to the surface via an annulus formed between the borehole wall and the drill bit. As the drilling fluid exits the bit, the fluid carries cuttings from the bit and the drilling fluid and cuttings are typically referred to as returns. Typically, the drilling fluid is a mud including a base fluid, typically water or oil, and various additives suspended, dissolved, and/or emulsified in the base fluid.
After drilling to a predetermined depth, the drill string and drill bit are removed and another tubular string of casing (or liner) is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is temporarily hung from the surface of the well. A cementing operation is then conducted in order to fill the annular area with cement. The casing string is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
A drilling rig is constructed on the earth's surface to facilitate the insertion and removal of tubular strings (i.e., drill strings or casing strings) into a wellbore. Alternatively, the drilling rig may be disposed on a jack-up platform, semi-submersible platform, or a drillship for drilling a subsea wellbore. The drilling rig includes a platform and power tools, such as a top drive, power tongs, and a spider, to engage, assemble, and lower the tubulars into the wellbore.
In order to drill and case the wellbore, it is necessary deploy tubular strings into the wellbore and may be necessary to remove tubular strings from the wellbore. Further intervention operations, such as fishing a broken or stuck tubular or tool, and workover operations also require deploying and removing tubular strings. When tubular strings are being run into or pulled from the wellbore, it is often necessary to fill the tubular string, take returns from the tubular string, or circulate fluid through the tubular string. This requires that the tubular string be threaded to the top drive (or Kelly hose) or be connected a circulation head. Previous circulation heads are firmly attached to the traveling block or top drive. In either case, precise spacing is required of the seal assembly relative to the tubular and elevators. In the case where slip-type elevators are used, the spacing of the seal could be such that when the elevators were near the upset of the tubular, the seal could be out of the tubular. When required, the slips at the rig floor must be set on the tubular and the traveling block or top drive lowered in order to move the seal into sealing engagement with the tubular. This requires that the running or pulling of the tubular stop until the slips were set at the rig floor and the seal engagement be made. This is not desirable when a well kick occurs or fluid is overflowing from the tubular.
In the case where “side door” or latching elevators are used, the seal must be engaged in the tubular prior to latching the elevators below the upset portion of the tubular. This requires that the seal be engaged in the tubular at all times that the elevators are latched on the tubular. When joints or stands of tubulars are racked back in the derrick, it is difficult to insert the seal into the tubular prior to latching the elevators with the top of the tubular far above the derrick man. Also, with the seal engaged in the tubular at all times, this is a disadvantage when there is a need to access the top of the tubular while the tubulars are in the elevators or when the tubular is being filled with fluid and the air in the tubular begins to be entrained in the fluid column rather than escaping the tubular. For example, if a high-pressure line was to be attached to the tubular and the tubular moved at the same time, all previous devices had to be “laid down” to allow a hard connection to be made to the tubular since they are in the way of the tubular connection.
Mudsaver valves are usually connected to the lower end of the top drive/Kelly or circulation head to prevent spillage of mud when the top drive/Kelly hose or circulation head are disconnected from the tubular. The use of a mudsaver valve is desirable to prevent the loss of mud, to prevent unsafe operating conditions for personnel, and to minimize contamination of the environment.